1. Field of the Invention
The present invention relates to an organic light emitting display device (OLED) and a method of fabricating the same and, more particularly, to an organic light emitting display device including an inorganic pixel defining layer that prevents outgas from the pixel defining layer from deteriorating an organic emission layer.
2. Discussion of the Background
Generally, an OLED is an emissive flat panel display device that electrically excites an organic compound to emit light. Hence, the OLED does not require a backlight unit, unlike a liquid crystal display (LCD). Therefore, the OLED may be made lightweight and thin using simplified processes. Also, the OLED may be fabricated at a low temperature, and it has a fast response speed of less than 1 ms, low power consumption, wide viewing angle, and high contrast. Accordingly, the OLED is attracting public attention as a next generation flat panel display device.
Generally, the OLED includes an organic emission layer between an anode and a cathode so that a hole supplied from the anode and an electron supplied from the cathode combine in the organic emission layer to form an exciton as a hole-electron pair, and the exciton returns to a ground state to generate energy, thereby emitting light.
An OLED may be a passive matrix or an active matrix OLED depending on how N×M pixels, disposed in a matrix, are driven. The passive matrix OLED has simpler manufacturing processes since its display region includes simple matrix type devices made of anodes and cathodes. However, its application may be limited to low resolution and small screen display devices due to problems of low resolution, high driving voltage, and reduced lifetime of the organic material. On the contrary, the active matrix OLED may be used for high resolution, large screen display devices since its display region includes thin film transistors formed in every pixel to supply a uniform current to the respective pixels to thereby obtain satisfactory brightness and low power consumption.
FIG. 1 is a cross-sectional view showing a pixel of a conventional OLED and a method of fabricating the same.
Referring to FIG. 1, a first electrode 110 is patterned and formed on a transparent substrate 100, which may be made of glass or plastic. When the first electrode 110 is an anode, it may be a transparent electrode made of indium tin oxide (ITO) or indium zinc oxide (IZO) having a high work function, or it may be a reflective electrode including a reflective layer made of a highly reflective metal such as Al, an Al alloy, or the like as its lower layer. When formed as a cathode, the first electrode 110 may be formed of a thin transparent electrode made of one material selected from a group consisting of Mg, Ca, Al, Ag, and an alloy thereof as a conductive metal having a low work function, or it may be a thick reflective electrode.
A pixel defining layer 120, which defines a pixel region, is formed of an insulating material on the first electrode 110 in order to insulate an organic emission layer. Typically, the pixel defining layer 120 is formed of an organic material such as polyimide (PI), polyamide (PA), acryl resin, benzocyclobutene (BCB), and phenol resin.
The pixel defining layer 120 may be deposited on the substrate using a spin coating method. Referring to FIG. 1, the pixel defining layer 120 has a thickness d of about 1 μm to 2 μm.
An opening 115 is formed in the pixel defining layer 120 to expose a portion of a surface of the first electrode 110 using a dry etching process.
Then, an organic layer 130, including at least an organic emission layer, is formed on the pixel defining layer 120 and on the exposed first electrode 110. The organic layer 130 may further include at least one of a hole injection layer, a hole transport layer, a hole blocking layer, an electron transport layer, and an electron injection layer in addition to the organic emission layer. The organic emission layer may be made of a low molecular weight material such as, for example, aluminum-tris-quinolate (Alq3), anthracene, and cyclo pentadiene, or a polymer material such as, for example, poly-(p-phenylenevinylene) (PPV) and its derivatives, polythiophene and its derivatives, and polyphenylene (PPP). The organic layer may be formed by a spin coating method and then patterned.
A second electrode 140 is formed on the entire surface of the organic layer 130. The second electrode 140 may be a reflective electrode made of one selected from a group consisting of Mg, Ca, Al, Ag and an alloy thereof, as a conductive metal having a low work function, when the first electrode 110 is a transparent anode or a transparent electrode including a reflective layer, and may be formed of a transparent electrode such as ITO or IZO when the first electrode 110 is a cathode. The second electrode 140 may be formed by a vacuum deposition method.
However, when the pixel defining layer 120 is formed of an organic material, outgassing of H2O, O2 and so on from the pixel defining layer into the organic layer 130 may deteriorate the organic layer 130, thereby increasing pixel shrinkage and decreasing the OLED's lifetime.